The present invention relates generally to precision motion devices. More particularly, the present invention relates to precision stages configured for moving or carrying an object to be processed. Even more particularly, the present invention relates to techniques for preventing performance degrading forces from acting on a high precision stage.
High precision stages for moving an object to be processed are generally well known. These stages are typically used in manufacturing and inspection machines where precise movements are needed to position an object. The movements may include moving the stage to a fixed position or moving the stage over a specific trajectory, e.g., scanning or step/repeat. By way of example, high precision stages have been introduced and employed to various degrees to position a substrate such as a reticle, mask and/or wafer in semiconductor processing equipment. Semiconductor processing generally requires precise tolerances in order to achieve finer geometries and therefore the stages must be capable of precisely locating the substrate relative to the processing part of the equipment. For example, the processing part may be an inspection system for inspecting the surface of the substrate or a lithography system for writing a circuit image onto a wafer. As should be appreciated, an out of position or mis-aligned substrate may cause errors in inspecting or writing, especially with the extreme level of accuracy that is sought with today's ever shrinking circuit dimensions.
Many high precision stage designs require cables and hoses to be attached to the moving part of the stage. Cables are typically required for actuator power, sensor signals and the like. Hoses, on the other hand, are frequently required for cooling actuators or work pieces, providing pressurized air or fluid for aerostatic or hydrostatic bearings, providing vacuum or return fluid for the same bearings, or providing vacuum for work piece chucking. By way of example, FIG. 1A illustrates a simplified diagram of a prior art stage system 10 for moving a work piece 11. Stage system 10 typically includes a stage 12 that is movably coupled to a guide surface 13 of a rigid structure 14 and linearly positioned by a drive mechanism 16. As shown, the drive mechanism 16 provides a force F for driving the stage 12 back and forth. Furthermore, a plurality of cables and hoses 18 are attached between the rigid structure 14 and the stage 12 so as to connect external devices (not shown) to the moving stage 12. For example, the cables may be electrical cables or fiber optic cables and the hoses may be cooling hoses, air hoses or vacuum hoses. Typically, such cable/hose assemblies are pushed and pulled by the movement of the stage.
By way of another example, FIG. 1B illustrates a simplified dual stage system 20 that includes both a coarse stage 22 and a fine stage 24 for moving a work piece 11. As the names suggest, the coarse stage makes large movements with low positioning accuracy while the fine stage makes small movements with high positioning accuracy. The coarse stage 22 is movably coupled to a guide surface 13 of a rigid structure 14 and linearly positioned by a first drive mechanism 26. The fine stage 24, on the other hand, is located on the coarse stage 22 and independently controlled via a second drive mechanism 28. As shown, the first drive mechanism 26 provides a force F1 for driving the coarse stage 22 back and forth and the second drive mechanism 28 provides a force F2 for driving the fine stage 24 back and forth. Furthermore, a plurality of first cables and hoses 34 are attached between the rigid structure 14 and the coarse stage 22 so as to connect external devices to the moving coarse stage 22, and a plurality of second cables and hoses 36 are attached between the coarse stage 22 and fine stage 24 so as to connect first cable and houses 34 to the moving fine stage 22. The travel between the coarse stage and the rigid structure is typically large and therefore the length of the first cable and hoses 34 are also large. The travel between the fine stage and the coarse stage is typically small and therefore the length of the second cables are also small.
Unfortunately, the cables and hoses, which are attached to the coarse stage and/or the fine stage, may impose a significant amount of drag and mechanical forces, both steady and impulsive, on the moving stage, thus degrading achievable performance. The forces may arise from the acceleration and de-acceleration of the stage (e.g., 4 g), the bending of cables or hoses, friction between adjacent cables or hoses, crossing of cables or hoses, the flexible dynamics of the hose and/or cables, i.e., some are relatively stiff, and the like. Some components of these forces are predictable and repeatable, and some components are not. As should be appreciated, these forces act as disturbances (both linearly and non-linearly) that may disturb the desired stage movement. For example, these forces may disturb the motion of the stage by pulling or pushing on the stage thus increasing settling times of the stage or producing excessive vibrations in the stage.
In the case that the instrument or machine is an ordinary machine tool, it is not necessary to consider the influence of such disturbances on the machine. However, in the case that the instrument is a high precision tool such disturbances give a fatal influence to those instruments. For example, in lithography systems, which require high positioning accuracy of the stage while moving, these cable and hose disturbances may impact the achievable accuracy of the stage and thus they may cause degradation in pattern placement and accuracy.
Accordingly, there have been some efforts to prevent drag and mechanical forces from acting on high precision stages, and more particularly on high precision stages used in lithography systems such as optical lithography and electron beam projection lithography. One solution has been to provide a stage system that includes both a coarse stage and a follower stage. The coarse stage moves the object to be processed to the desired processing location while the follower stage, following the coarse stage, carries the cable and hoses.
By way of example, FIG. 1C illustrates a simplified stage system 40 that includes both a stage 42 for moving a work piece 11 and a follower stage 44 for carrying a plurality of first cable and houses 46. Both stages 42, 44 are movably coupled to a guide surface 13 of a rigid structure 14 (i.e., stage frame). The stage 42 is linearly positioned by a first drive mechanism 50 and the follower stage 44 is linearly positioned by a second drive mechanism 52. As shown, the first drive mechanism 50 provides a force F1 for driving the stage 42 back and forth and the second drive mechanism 52 provides a force F2 for driving the follower stage 44 back and forth. Further, a plurality of first cables and hoses 46 are attached between the rigid structure 14 and the follower stage 44 so as to connect external devices to the moving follower stage 44, and a plurality of second cables and hoses 48, which are shorter than the first cable and hoses 46, are attached between the follower stage 44 and coarse stage 42 so as to connect first cable and houses 46 to the moving coarse stage 42. As should be appreciated, most of the cable drag forces act on the follower stage (e.g., long cables) and thus the disturbance forces on the coarse stage are due only to the small position differences between the coarse stage and the follower stage.
Although such designs work well, there are continuing efforts to improve techniques for preventing performance degrading forces from acting on a high precision stage. By way of example, in certain situations, it may not be desirable to have a follower stage. Follower stages, for example, typically require long travel bearings and actuators, which in turn requires additional space, power, and cost.